This invention relates generally to stress sensor gages and more particularly to a method and means for determining the presence of drift in the output signals of such gages.
While there are many applications for the well-known and conventional stress gage, one of the more important uses is in rocket engines. Stress gages are embedded in solid fuel rocket motors and from them it is possible to predict satisfactory performance after the fuel has been in storage for substantial lengths of time. There are, of course, other applications where a stress gage would be rendered inaccessible and this invention would apply.
The stress gage, embedded in a solid fuel rocket particularly, frequently suffer from what is referred to as "epoxy creep" or gage element slippage. This condition may be caused by a plurality of factors, however, the result of this and other internal and nonrelated factors, is drift in the output signal of the gage. This drift, particularly if relatively constant, is difficult to detect and often results in erroneous test readings.
The invention presented hereinafter is particularly adapted to overcome the disadvantages of the prior art by enabling more accurate and reliable stress measurements to be obtained from an embedded or inaccessible stress gage.